Windows Media Player problem

It started I’m not sure when (at least a few months ago).
I currently have Windows Media Player 9 and ATI File Player installed as well as a few codec packs.

Now my problem is that many movies/videos that worked fine before (and I mean a few YEARS before) now play sluggish (1 second per 3 seconds real time or so) and the sound as well is slow when playing in Windows Media Player. I usually play it in ATI File Player instead and it plays fine, although sometimes, my whole video card crashes while trying to play said video (VPU recover allows me to keep running, although I have to reboot anyway) at a random time during playback (sometimes 10 seconds in, other times over 40 seconds in).
Now one thing I noticed that are common to most of the problematic files is that they’re all encoded with Windows Media Video and Windows Media Audio (some are WM video/audio 5 while others are WM video/audio 9 codecs) so I’m guessing it’s my codecs that are at fault.

Thus I downloaded the official WM codecs from microsoft and installed them over the ones I already had. Now I did notice that some (note SOME (as in 1 or 2)) now work, but most others still don’t, including ones with WM codecs 9 encoding.

First of all, I don’t understand why Windows Media Player can’t play them while ATI File Player can.
Second, if it isn’t the codec that is the problem, what is?

PS: I have a P4-2.7 GHz w/ a Radeon 9600SE and 1 Gb RAM so I doubt my computer can’t support it (but I still can’t understand why my video card crashes when trying to play some movies... )

Please help

Yep, getting excately the same problem, files will play fine in Quicktime, Divx etc but media player (10) runs in slo-mo, though not all the time. I can’t put my finger on which app it is but have a feeling it is since I updated Nero burning Rom. Ocassionaly having run a game it works fine but as soon as reboot the problem comes back. I have 1Gb Ram, 3GHz and ATI 9800 so not specs of machine!